Hi, if you are selling and want the floor to look good, I’ve done this and it works. I work at a pub and had the same problem, I used kettle descaler solution mixed with hot water in a spray bottle, it works, cleans the grout up lovely as well, down side the room will smell of sick, so open windows, then I covered the tiles in red quarry tile polish (wax version not liquid - obtained on line) and polished and buffed using attachments on my orbital sander, the floor looked brand new, let me know how you get on xxx